You begin in the back of the truck. After it travels a short distance (passing two guards walking down the road) jump out and move down the hill. Think about marking the two patrolling guards to keep tabs on them later.
Head into the booth and collect the goodies on the ground. Stay crouched so the two guards don't see you there. When they've passed, climb up the tower, melee the lone guard and turn on the spotlight as instructed.
It might take a few minutes for him to appear, but use the spotlight to tag any soldiers you see. When you look at the target, he'll be tagged like everyone else. Stay in the tower and let him move closer to you. Even when he and another guard stop underneath the tower, stay out of sight. The target will tell his buddy to go see the CO.
Climb down and knock the target unconscious. Throw him over your shoulder and take him between the tents in the middle of the area you're in. Kick him in the body to wake him up, then put him in a hold to interrogate him. When you're done, knock him out and then shoot him with a tranquillizer dart. It might seem like overkill, but unconscious targets can wake up.
You're headed to the central control tower. Go through the gate to the left. It should be open. Just make sure to avoid the guards and head in the direction of your objective marked on-screen.
After you go through a gate, you'll enter an open area covered in concrete. There is a lone guard patrolling on the left side. Take him out with tranquillizer dart and stash the body near a parked jeep. Drop down into the nearby vent and follow it to an opening covered with bars. Crawl back out and pick the nearby locked door to enter the next area.
There's a guard patrolling a short distance away. Tag him and then climb the ladder to the right when you go through the gate. Crawl along the catwalk and enter the central tower to retrieve the tape. Take a moment to tag a nearby armored vehicle before you move on.
Head back the way you came and climb down the ladder. Head to the right (when your back is against the ladder), making sure you avoid the guard you tagged earlier. Move forward and down a ramp into an underground area. Move through it and up some stairs, coming to a door with bars on the window. Wait patiently for both guards to move away before going through the door and taking cover to the left.
Move left until you come to another wall. Drop down into the vent and crawl through until you emerge near a building. Crawl under the building, being careful not to alert the guard. Move to the armored vehicle nearby and get in. Drive it under the bridge, stopping and exiting when you reach a dirt road on your left. Call a chopper to the nearest landing zone and meet it there to complete the mission.